They are really two different cameras. the Sealife 1200 is strictly a point and shoot camera, while the DX-1g can be used as a poiht and shoot camera but can also be used in full manual mode. If you want to progress in your underwater photography, then you will want to have a camera that shoots in manual mode. Manual mode gives you much more artistic effect when taking a picture. The DX-1g also has very little lag time between when you push the shutter and when the camera takes the picture. You should check to see what the shutter lag time is for the Sealife camera. The DX-1G camers comes with a 24-72 mm lens which means that without any add-on lenses, the camera comes with a wide angle capability. The macro mode is also better on the DX-1G. The Sealife macro works from 4 inches to 3 feet, while the DX-1G works from 1 cm (about 1/2 inch) to infinity.
If all you want is a point and shoot camera, then you should compare pictures taken with the DX-1G with those from the Sealife camera. You also need to consider shutter lag as well. Shutter lag is huge. If you have a short shutter lag, you can compose the shot and know that when you push the shutter, you will capture what you see. If the shutte lag is long, then you must lead your subject so that when you push the shutter, you anticipate that the subject will move to a point when the picture is taken.
If you click on my "photos" link you will see pics taken with the DX-1G (Fiji 2010, Eluthera, Turks and Caicos, Galapagos). The galapagos pics were the first ones taken with the camera and while they came out alright, I was still learning how to use the camera.
Regards,
Bill